oxygen evolution reaction and oxygen reduction reaction (OER and ORR) play important roles in rechargeable zinc-air battery (ZAB), whereas OER and hydrogen evolution reaction (HER) are the core reactions in EWS. [4,5] These electrochemical reactions exhibit sluggish kinetics because they require multistep protoncoupled electron transfers, which increase the overpotentials of the systems, thus causing the losses of considerable energy and long-term electrocatalytic activity. [6][7][8][9] Multifunctional electrocatalysts that efficiently catalyzes diverse electrochemical reactions (OER, HER, and ORR) have recently attracted considerable attention. Multifunctional electrocatalysts can reduce the manufacturing cost of the specific electrocatalysts for various electrochemical systems. The state-of-the-art catalysts such as Pt-based electrocatalysts (ORR and HER), IrO 2 and RuO 2 (OER) could not meet the characteristics of ideal multifunctional electrocatalysts because of high cost, non-abundancy, and non-multifunctional electrocatalytic activity. [10] Moreover, there are limited reports on the strategies for synthesizing multi functional electrocatalysts with intense activity, stability, and selectivity; [11][12][13] and this has necessitated the development of inexpensive, abundant, efficient, and stable multifunctional electrocatalysts to substitute the noble metal-based electrocatalysts.Transition metal oxides (TMOs) have been recently identified as the most promising alternatives to noble metal-based electrocatalysts because of their natural abundance, environmental sustainability, and superior thermal and chemical stabilities under different operating conditions. [14][15][16][17][18] A few promising TMOs exhibit spinel structures, especially cobalt oxide, because Co in its d 7 state with unpaired electrons enhances the activation and polarization of media and the presence of different valences encourage electron transfer during ORR, OER, and HER. Similarly, manganese oxides are inexpensive and abundant materials that promote natural OER in plants, as well as the desired four-electron pathway toward ORR; however, the poor electronic conductivity of manganese oxides limits their electrocatalytic activity. To overcome these limitations, manganese oxide can be combined with cobalt as a co-metal in the spinel structure. Further, increasing the surface area and amounts of Mn 3+ and Mn 2+ can considerably enhance the The integration of energy conversion and storage systems such as electrochemical water splitting (EWS) and rechargeable zinc-air battery (ZAB) is on the vision to provide a sustainable future with green energy resources. Herein, a unique strategy for decorating 3D tetragonal CoMn 2 O 4 on carbon cloth (CMO-U@CC) via a facile one-pot in situ hydrothermal process, is reported. The highly exposed morphology of 3D tetragons enhances the electrocatalytic activity of CMO-U@CC. This is the first demonstration of such a bifunctional activity of CMO-U@CC in an EWS system; it achieves a nominal cell voltage of 1.610 ...

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To enhance the efficiency of hydrogen production, bimetallic oxides with spinel structures, M2GeO4 (M = Fe, Co), were synthesized via a facile one-pot hydrothermal method and were used as electrocatalysts...

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Single-atom catalysts (SACs), as the name suggests, indicate that only one element participates in the catalytic reaction. The characteristic feature of SACs is that it has immobilized active sites with specific properties, such as unexpected catalytic activity, high product selectivity, and reduced energy barrier. SACs for electrochemical CO2 reduction reactions (CO2RR) should have isolated metal atoms acting as active sites to maximize the efficiency of metal use. Conventional metal catalysts with nano-sized metal particles, however, contain a variety of inactive sites showing inferior efficiency of metal use. Therefore, systematic synthesis and analysis of high-efficiency SACs have been an interesting challenge in the CO2RR. To address these issues, many researchers have attempted to synthesize SACs through various methods and employed numerous characterization techniques to identify single atoms and their electrochemical properties. In this review, we discuss recent trends in the synthesis strategies and analyzing techniques of SACs and explain the influence of SACs on electrochemical CO2RR mechanisms of various C1 and C2 products.